regex – 是否有正则表达式来检测有效的正则表达式？

/
^                                             # start of string
(                                             # first group start
  (?:
    (?:[^?+*{}()[]|]+                      # literals and ^,$
     | .                                    # escaped characters
     | [ (?: ^?. | ^[^] | [^^] )     # character classes
          (?: [^]]+ | . )* ]
     | ( (?:?[:=!]|?<[=!]|?>)? (?1)?? )  # parenthesis,with recursive content
     | (? (?:R|[+-]?d+) )                 # recursive matching
     )
    (?: (?:[?+*]|{d+(?:,d*)?}) [?+]? )?   # quantifiers
  | |                                        # alternative
  )*                                          # repeat content
)                                             # end first group
$                                             # end of string
/

这是一个递归正则表达式，并且不受许多正则表达式引擎支持。基于PCRE的应该支持它。

没有空格和注释：

/^((?:(?:[^?+*{}()[]|]+|.|[(?:^?.|^[^]|[^^])(?:[^]]+|.)*]|((?:?[:=!]|?<[=!]|?>)?(?1)??)|(?(?:R|[+-]?d+)))(?:(?:[?+*]|{d+(?:,d*)?})[?+]?)?||)*)$/

.NET不直接支持递归。 ((？1)和(？R)构造)。递归必须转换为计数平衡组：

^                                         # start of string
(?:
  (?: [^?+*{}()[]|]+                   # literals and ^,$
   | .                                  # escaped characters
   | [ (?: ^?. | ^[^] | [^^] )   # character classes
        (?: [^]]+ | . )* ]
   | ( (?:?[:=!]
         | ?<[=!]
         | ?>
         | ?<[^Wd]w*>
         | ?'[^Wd]w*'
         )?                               # opening of group
     (?<N>)                               #   increment counter
   | )                                   # closing of group
     (?<-N>)                              #   decrement counter
   )
  (?: (?:[?+*]|{d+(?:,d*)?}) [?+]? )? # quantifiers
| |                                      # alternative
)*                                        # repeat content
$                                         # end of string
(?(N)(?!))                                # fail if counter is non-zero.

压缩：

^(?:(?:[^?+*{}()[]|]+|.|[(?:^?.|^[^]|[^^])(?:[^]]+|.)*]|((?:?[:=!]|?<[=!]|?>|?<[^Wd]w*>|?'[^Wd]w*')?(?<N>)|)(?<-N>))(?:(?:[?+*]|{d+(?:,d*)?})[?+]?)?||)*$(?(N)(?!))